Strip for packing module, corresponding module and column

ABSTRACT

The invention concerns a corrugated packing module for treating a fluid delimited by two channels ( 18 ). It comprises a running zone ( 4 ) whereof the channels define ridge lines ( 26 ) having a global sloping direction (D 1 ) relative to a general direction of circulation (D f ) of the fluid. The strip comprises a transition zone ( 6, 8 ) adjacent to the running zone ( 4 ). Each ridge line ( 26 ) of the transition zone ( 6, 8 ) extends inside a specific zone centered on a curve (A) which extends tangentially the ridge line ( 26 ) of the running zone ( 4 ). The radial width (Lr) is 10% of the corresponding radius of curvature of the curve (A). The radius of curvature (Rc) of the curve (A) is at all points 1.5 times greater than the hydraulic diameter (Dh) of a channel ( 18 ). The invention is applicable to air distillation columns.

The present invention relates to a corrugated strip made of sheetmaterial, especially plastically deformed sheet metal, for a packingmodule for treating a fluid, of the type defining flow channels for thefluid and comprising a spanning region, the channels of which define, inside view, peak/trough lines having a general direction inclined to ageneral flow direction of said fluid, the strip furthermore including atleast one transition region adjacent to the spanning region, thedirection of the peak/trough lines of which transition regionprogressively approaches the general flow direction of said fluid.

The term “packing” is understood to mean a device intended for mixing aphase and/or for bringing several phases flowing cocurrently orcountercurrently into contact with one another. A heat and/or massexchange and/or a chemical reaction may in particular take place in thepacking. One particular application of the invention lies in the columnsfor separating gas mixtures, especially air distillation columns.

Mentioned in the prior art are air distillation installations comprisingcross-corrugated packing modules, which are also called packs. Themodules comprise corrugated strips or metal sheets placed vertically ina parallel fashion, the corrugations of which sheets are oblique withrespect to a general fluid flow direction in the installation, and areinclined alternately, generally crossed at 90°, from one sheet toanother.

The packing modules are slipped into the distillation column so that thesheets of one module are angularly offset with respect to the sheets ofan adjacent module about the axis of the column, generally by 90° fromone module to another.

During use, the gas is constrained to change direction at such an anglein order to flow from one module to another, with a corresponding headloss at this location. Such a head loss causes accumulation of liquid inthe lower region of the upper module and flooding of the column at thislocation, whereas the central portion of the modules has not yet reachedits flooding point. This phenomenon reduces the treatment capacity ofthe column.

To reduce this effect, it has been proposed in the prior art to usepacking modules having a structured interface region.

Such a packing module is disclosed, for example, in WO-A-97/16247.

In this module, the packing strips comprise, in their marginal regions,corrugations with curved peaks that extend, along the edge facing anadjacent module, parallel to the general flow direction of the fluids.

These curved corrugations join this edge of the strip to thecorrugations lying in the spanning region of the module, which lieobliquely relative to the general flow direction of the fluids.

However, the packing strips disclosed in the aforementionedWO-A-97/16247 still generate a substantial head loss in the interfaceregions of the modules.

The object of the invention is to propose a packing module whose headloss is further reduced.

For this purpose, the subject of the invention is a corrugated strip ofthe aforementioned type, characterized in that each peak/trough line ofthe transition region, in side view, lies within a defined area centeredon a curve that tangentially extends the peak/trough line of thespanning region and the radial width of which area is 10% of thecorresponding radius of curvature of the curve, and in that the radiusof curvature of the curve is at any point greater than 1.5 times,preferably greater than 1.6 times, the hydraulic diameter of a channel.

According to particular embodiments, the strip according to theinvention may comprise one or more of the following features:

-   -   the radius of curvature of the curve is greater than three times        the hydraulic diameter of a channel;    -   the radius of curvature of the curve is less than five times the        hydraulic diameter of a channel;    -   the curve is a circular arc;    -   the center of the circular arc is located on the edge of the        strip or on an extension of this edge;    -   the curve comprises at least two circular arcs of different        radii of curvature, the circular arcs being joined together in        the order of increasing value of their radius of curvature        starting from the edge of the strip;    -   the edge direction of the peak/trough lines at the point of        their intersection with the edge of the strip is substantially        the general direction of flow of said fluid;    -   the peak/trough lines of the transition region consist of at        least two straight segments especially of identical lengths; and    -   the peak/trough lines of the transition region coincide with the        curve.

The subject of the invention is also a packing module for a materialand/or heat exchange column, characterized in that it comprises a stackof strips as defined above, with the general directions of theirpeak/trough lines of their spanning region reversed from one strip toanother.

According to one particular embodiment of the module, the packingdensity is greater than 300 m²/m³, and preferably greater than 400m²/m³.

The subject of the invention is also a cryogenic distillation column,especially for the distillation of air, characterized in that itcomprises at least one packing module as defined above.

The invention will be more clearly understood on reading the descriptionthat follows, given solely by way of example and with reference to theappended drawings, in which:

FIG. 1 is a schematic side view of a packing strip according to theinvention;

FIG. 2 is a sectional view on the line II-II of FIG. 1, on a largerscale;

FIGS. 3 and 4 are graphs showing the behavior of one example of apacking module according to the invention compared with packing modulesof the prior art; and

FIG. 5 is a side view of part of an alternative embodiment of a packingstrip according to the invention, on a larger scale.

FIG. 1 shows, in side view, a packing module 2 according to theinvention. The packing module 2 is intended to be mounted in a fluidtreatment column with a vertical central axis (not shown). Duringoperation of the column, fluid flows over the surface of the strip 2 ina general fluid flow direction Df, which in this case is vertical. Thepacking strip 2 is manufactured from a smooth sheet-metal strip and isplastically deformed by bending.

The packing strip 2 has a corrugated spanning region 4 to whichcorrugated upper 6 and lower 8 transition regions join along thedirection Df. Each transition region 6, 8 terminates in a horizontaledge 10, 12. In the mounted state of the strip 2, the transition regions6, 8 are adjacent neighboring packing modules, which consist of stripswhich are similar but angularly offset about the central axis of thecolumn.

FIG. 2 shows a sectional view of the spanning portion 4 on the lineII-II of FIG. 1. The strip 2 consists of a succession of flat surfaces14, 16 that are inclined to the plane of FIG. 1, alternately to thefront and to the rear. Two neighboring surfaces 14, 16 form a fluid flowchannel 18 between them. Each channel 18 has an approximately triangularcross section and is closed along two sides and open along the thirdside. The surfaces of a channel 14, 16 make a bending angle γ, which inthis case is 60°. The channels 18, and therefore the strip, have athickness E. The flat surfaces 14, 16 have curved linking areas 22, 24that link two adjacent surfaces 14, 16. These linking areas have aradius of curvature r. The linking areas 22, 24 form, in side view (FIG.1), peak 26 and trough 28 lines. In side view, two neighboring peaklines 26 or two neighboring trough lines 28 lie parallel to each otherand are separated by a distance B, which is the pitch of thecorrugation. The peak 26/trough 28 lines of the spanning region 4 arestraight and lie along a direction D_(i). This direction makes an angleδ=45° to the edges 10, 12 of the strip and to the direction D_(f). Theangle δ is generally between 30° and 60°.

Unlike the spanning region, the channels 18 of the transition regions 6,8 are curved. More precisely, the peak 26/trough 28 lines of thechannels 18 lie approximately in the direction D_(i) in an area joinedto the spanning region 4 and progressively change their inclinationtoward an edge inclination direction D_(b) at the location of the edge10, 12 of the strip. In the present embodiment, each peak 26/trough 28line has, in the transition regions, in side view, the shape of acircular arc A of radius Rc. The center C of each circular arc A islocated on the edge 10, 12 of the strip or on an extension of said edge,in such a way that the direction D_(b) is identical to the directionD_(f). Each circular arc A joins a peak 26/trough 28 line of thespanning region 4 tangentially. Each of the upper 6 and lower 8transition regions has a height Hc, measured along the direction D_(f).The height Hc as a function of δ is Hc=Rc×cosδ.

The hydraulic diameter of each channel 18 of the spanning region 4 is:${Dh} = {\frac{4 \times {channel}\quad{cross}\quad{section}}{{channel}\quad{perimeter}}.}$

If each channel 18 is defined by two V-shaped surfaces 14, 16, that isto say neglecting the radius r, the hydraulic diameter of a channel (18)is:Dh=B×cos(γ/2).The radius Rc of each arc A is greater than 1.5 times the hydraulicdiameter Dh. In practice, it is between 1.6 Dh and 5 Dh, and ispreferably about 3 Dh.

FIG. 3 shows curves comparing the capacities of two packings of theprior art and one packing according to the invention. Each packing has adensity of 500 m²/m³. The angle of inclination of the channels in thespanning region δ is 45°. Plotted on the x-axis is the maximumthroughput per unit area of the gas, plotted on the y-axis is the headloss per unit length.

Curve C1 shows the capacity of a first conventional packing, with notransition regions, namely a packing consisting of corrugated stripsthat are formed only by a spanning region. Curve C2 indicates thecapacity of a second packing, having two, lower and upper, transitionregions, the Rc/Dh ratio of which is equal to 1. For a head loss of 10mbar/m, a 25% increase in capacity over the conventional packing isobserved.

Curve C3 indicates the capacity of a packing according to the invention,the Rc/Dh ratio of which is 3. For a head loss of 10 mbar/m, thecapacity is further increased by 12% over the second packing.

FIG. 4 shows curves comparing the behavior of the aforementionedpackings. Plotted on the x-axis is the degree of flooding of thepacking, while plotted on the y-axis is the head loss per unit length.

Curve C4 shows the behavior of the conventional first packing. Curve C5indicates the behavior of the second packing and curve C6 indicates thebehavior of the third packing. For a head loss of 6 mbar/m, the capacityis increased by 8% for a packing with Rc/Dh=3, compared to a packingwith Rc/Dh=1.

FIG. 5 shows a portion of a transition region of an alternativeembodiment of a packing strip according to the invention.

Unlike the first embodiment, the angle of inclination 6 of the peak26/trough 28 lines of the spanning region 4 is 30°. Consequently, theyare inclined at 60° to D_(f). In addition, the peak 26/trough 28 linesin the transition region 8 are made up of three straight segments 36,38, 40 of identical length 1. The successive segments 36, 38, 40 areinclined, from the spanning region to the edge, by δ₁=39°, δ₂=58° andδ₃=77° to the edge 12.

Each peak 26/trough 28 line of the strip 2 lies, in the transitionregion 8, within an area 42 that is defined as follows:

A curve in the form of a circular arc A joins the terminal point T1 ofthe peak 26/trough 28 line in question of the spanning regiontangentially.

This circular arc A has a radius Rc of at least 1.5 times, preferably atleast 1.6 times, the hydraulic diameter Dh of the channels 18 of thestrip 4.

At the point of intersection T2 of the circular arc A with the edge 12,this circular arc has a tangential direction D_(t) that is more inclinedto the general flow direction D_(f) of the fluid than the peak 26/trough28 lines of the spanning region 4.

The area 42 has a radial width Lr that is 10% of the radius Rc. The area42 is centered on the circular arc A, in such a way that it extends by5%×Rc on either side of the circular arc A.

It should be noted that this circular arc A is the ideal line ofcurvature for a peak 26/trough 28 line lying within the area 42.

It has been observed that a packing module manufactured from a packingstrip according to the invention exhibits an increased capacity.

The packing modules manufactured from strips according to the inventionpreferably have a packing density a of greater than 300 m²/m³ andpreferably greater than 400 m²/m³.

It should be noted that the hydraulic diameter Dh can also be calculatedapproximately as a function of the packing density a according to theformula: Dh=4/a.

The modules comprising a stack of packing strips according to theinvention are, for example, used in cryogenic distillation columns,especially for air distillation.

As a variant, the curve defining the area 42 may have a variable radiusof curvature, especially one that decreases from the spanning region ofthe strip. In particular, it may consist of a plurality of circular arcsof different radii of curvature. For example, it may consist of twocircular arcs having radii of curvature Rc of 1.5 Dh and 2 Dh.Preferably, the circular arcs extend from the edge in the increasingorder of their radii of curvature (to be confirmed by Mr Werlen).

1-12. (canceled).
 13. An apparatus which may be used for treating afluid in a packing module comprising a corrugated strip of sheetmaterial, said strip further comprising: a) flow channels for saidfluid; b) a spanning region wherein said channels define spanningpeak/trough lines with a general direction (Di) substantially opposed toa general flow direction (Df) of said fluid; and c) at least onetransition region located adjacent to said spanning region and furthercomprising: 1) said channels defining transition peak/trough lines witha direction that progressively approaches said general flow direction(Df) of said fluid; 2) a curve (A) that said transition peak/troughlines substantially follow, said curve tangentially extending from saidspanning peak/trough lines; and 3) a radius of curvature (Rc) of saidcurve (A) that at any point is greater than about 1.5 times thehydraulic diameter (Dh) of said channel.
 14. The apparatus of claim 13,wherein each transition peak/trough line lies within a defined areacentered on said curve (A).
 15. The apparatus of claim 14, wherein saidarea has a radial width (Lr) of about 10% of the corresponding radius ofcurvature (Rc).
 16. The apparatus of claim 13, wherein said sheetmaterial comprises metal which is plastically deformed.
 17. Theapparatus of claim 13, wherein said radius of curvature (Rc) of saidcurve (A) is greater than about three times said hydraulic diameter (Dh)of said channel.
 18. The apparatus of claim 17, wherein said radius ofcurvature (Rc) of said curve (A) is greater than about 3 times saidhydraulic diameter (Dh) and less than about five times said hydraulicdiameter (Dh) of said channel.
 19. The apparatus of claim 13, whereinsaid curve (A) is a circular arc.
 20. The apparatus of claim 19, whereinthe center (C) of said circular arc is located on the edge of said stripor on an extension of the edge.
 21. The apparatus of claim 13, whereinsaid curve (A) comprises at least two circular arcs of different radiiof curvature, said arcs being joined together in the order of increasingvalue of their radius of curvature starting from the edge of said strip.22. The apparatus of claim 13, wherein the edge direction (D_(b)) ofsaid transition peak/trough lines at the point of their intersectionwith the edge of said strip is oriented in substantially the same saidgeneral direction of flow (D_(f)) as said fluid.
 23. The apparatus ofclaim 13, wherein said transition peak/trough lines consist of at leasttwo straight segments of identical lengths (l).
 24. The apparatus ofclaim 13, wherein said transition peak/trough lines coincide with saidcurve (A).
 25. An apparatus which may be used for a packing module in amaterial and/or heat exchange column comprising a stack of corrugatedstrips, said strips further comprising: a) flow channels for said fluid;b) a spanning region wherein said channels define spanning peak/troughlines with a general direction (Di) substantially opposed to a generalflow direction (Df) of said fluid; and c) at least one transition regionlocated adjacent to said spanning region and further comprising: 1) saidchannels defining transition peak/trough lines with a direction thatprogressively approaches said general flow direction (Df) of said fluid;2) a curve (A) that said transition peak/trough lines substantiallyfollow, said curve tangentially extending from said spanning peak/troughlines; and 3) a radius of curvature (Rc) of said curve (A) that at anypoint is greater than about 1.5 times the hydraulic diameter (Dh) ofsaid channel.
 26. The apparatus of claim 25, wherein said generaldirection of said spanning peak/trough lines is reversed from one stripto another.
 27. The apparatus of claim 25, wherein the packing densityLa) of said stack is greater than about 300 m²/m³.
 28. An apparatuswhich may be used for the cryogenic distillation of air, comprising atleast one packing module, said packing module further comprising a stackof corrugated strips, said strips further comprising: a) flow channelsfor said fluid; b) a spanning region wherein said channels definespanning peak/trough lines with a general direction (Di) substantiallyopposed to a general flow direction (Df) of said fluid; and c) at leastone transition region located adjacent to said spanning region andfurther comprising: 1) said channels defining transition peak/troughlines with a direction that progressively approaches said general flowdirection (Df) of said fluid; 2) a curve (A) that said transitionpeak/trough lines substantially follow, said curve tangentiallyextending from said spanning peak/trough lines; and 3) a radius ofcurvature (Rc) of said curve (A) that at any point is greater than about1.5 times the hydraulic diameter (Dh) of said channel.
 29. The apparatusof claim 28, wherein said general direction of said spanning peak/troughlines is reversed from one strip to another.
 30. The apparatus of claim28, wherein the packing density La) of said stack is greater than about300 m²/m³.